Produced sound from speakers has become so common and integrated in our daily lives it is often taken for granted. Living with inventions such as televisions, phones and radios, chances are you rarely ever have days with nothing but natural sounds. Yet, few people know the physics involved in the technology that allows us to listen to music in our living room although the band is miles away. This article will investigate and explain the physics and mechanism behind loudspeakers – both electromagnetic and electrostatic.
The Physics of Sound
To understand how loudspeakers work it is necessary to know some basic sound physics.
Sound is essentially a wave produced by a vibrating source. This compression and rarefaction of matter will transfer to the surrounding particles, for instance air molecules. Rhythmic variations in air pressure are therefore created which are detected by the ear and perceived as sound. The frequency of a sound wave is the number of these oscillations that passes through a given point each second. It is the compression of the medium particles that actually constitute a sound wave, and which classifies it as longitudinal. As opposed to transverse waves (eg. light waves), in which case the particles move perpendicular to the direction of the wave movement, the medium particles are moving in the same or opposite direction as the wave (Russell, D. A., 1998).
Compression and rarefaction of particles forming sound waves. Retrieved 23/02/14 from Popular Science Monthly Volume 13
What distinguishes sound waves from most other waves is that humans easily can perceive the frequency and amplitude of the wave. The frequency governs the pitch of the note produced, while the amplitude relates to the sound level which is measured in decibels (dB).
Relationship between sound level and ambience, pitch and frequency. Retrieved 23/02/14 from http://californiaearthquakes.weebly.com/sound-waves--earthquakes.html
Static Electricity and Electromagnetism
The two types of speakers explained in this article are based on two different principles in physics – static electricity and electromagnetism. While electromagnetism concerns magnetic fields produced by moving charges, static electricity literarily means electricity staying still.
Shortly said, electrostatics is the branch of physics that concerns the force that charges exert on each other. The basic and most important principle regarding electrostatics is this: like charges repel and opposite charges attract. As with many other fundamental properties it is nearly impossible fully fathom the concept of charge; all we know is that objects and particles can have either positive or negative charges. Since protons are charged positively and electrons negatively, elements derived of its electrons are considered to have positive charge. Conversely, materials with excess electrons on the other hand are negatively charged. People have learnt to take advantage of the physical movement...